Relationship between insulin resistance and lipid peroxidation and antioxidant vitamins in hypercholesterolemic...

Several studies have reported that insulin resistance and compensatory hyperinsulinemia increased lipid peroxidation, suggesting the linking to each other. We investigated the relationships between insulin resistance index HOMA-IR and lipid peroxidation, plasma antioxidant status in non-diabetic, hypercholesterolemic patients.

We measured the urinary excretion of 8-epi-prostaglandin F(2)(alpha)(PGF(2)(alpha)) levels as a measure of lipid peroxidation in vivo, total radical trapping antioxidant potential (TRAP) and fat-soluble antioxidant vitamins in 76 non-diabetic subjects with hypercholesterolemia (mean age 59 years, 25 males and 51 females). Insulin resistance was evaluated by homeostasis model assessment (HOMA-IR) derived from fasting glucose and insulin concentrations.

HOMA-IR was positively correlated with the urinary excretion of PGF(2)(alpha) (r=0.222, p<0.05) and negatively correlated with the TRAP (r=-0.211, p<0.05) in total subjects. Furthermore, there were significant inverse relationships between HOMA-IR and lipid corrected fat-soluble vitamins such as beta-carotene (r=-0.297, p<0.01) and gamma-tocopherol (r=-0.243, p<0.05) and also significant inverse relation was found between lipid corrected beta-carotene and the urinary PGF(2)(alpha)excretion (r=-0.205, p<0.05). When total subjects were divided into three groups according to tertiles of HOMA-IR, significant differences in urinary PGF(2)(alpha)excretion (p<0.05) and lipid corrected beta-carotene (p<0.005) among the three groups were observed. The highest HOMA-IR group had the higher levels of urinary PGF(2)(alpha)excretion and lower levels of plasma beta-carotene compared with the lowest HOMA-IR group.

Our data showed that the insulin resistance of hypercholesterolemic patients increased oxidative stress and negatively influenced plasma antioxidant system. These results provide evidence in understanding mechanism linking insulin resistance and oxidative stress accompanied by reduced antioxidant system.